Either use bison with %glr-parser or flatten parenthesizedexpression and
castexpressiion to be a single rule and manually decide if it's a cast
or not later on. Your resulting grammar will be a mess. This is the
great ugly with lalr(1) parsers.

Would it be possible to build a tool that would take a grammar like this
and rewrite the rules, or at least try and rewrite the rules, to remove
these kinds of problems?